how can I convert irregular mesh into regular mesh. Any refrence thanks in advance prasat

I am not sure about your question, but if you mean smoothing an irregular quadrilateral or hexahedral structured mesh then you might get some ideas from a paper by J. Petera and J. F. T Pittman, "Isoparametric Hermite Elements," Int. J. Num. Meth. Engr. 37, 3489-3519 (1994). I think some of the ideas discussed at the end of Sect. 4 of a paper I have submitted for publication "II. Some Hermite Interpolation Functions for Solenoidal and Irrotational vector Fields," available on my web site j.t.holdeman.home.att.net under "research" might also be useful. There have also been papers on smoothing triangular meshes, but I lost track of these many years ago.